TY - JOUR
T1 - Brønsted Acids Promote Olefin Oxidations by Bioinspired Nonheme CoIII(PhIO)(OH) Complexes
T2 - A Role for Low-Barrier Hydrogen Bonds
AU - Sun, Dongru
AU - Wu, Zhimin
AU - Zhang, Xuan
AU - Yang, Jindou
AU - Zhao, Yufen
AU - Nam, Wonwoo
AU - Wang, Yong
N1 - Funding Information:
This work is supported by the National Natural Science Foundation of China (No. 21873052), the National Research Foundation (NRF) of Korea (No. NRF-2021R1A3B1076539 to W.N.), the Natural Science Foundation of Zhejiang Province (No. LQ20B030004), the Ningbo Natural Science Foundation (No. 202003N4079), the Scientific Research Grant of Ningbo University (No. 215-432000282), and the Ningbo Top Talent Project (No. 215-432094250). Y.W. acknowledges Professor Hui Chen at the Institute of Chemistry, CAS, for the fruitful discussion.
Publisher Copyright:
© 2023 American Chemical Society
PY - 2023/3/15
Y1 - 2023/3/15
N2 - Introduction of Brønsted acids into biomimetic nonheme reactions promotes the oxidative ability of metal-oxygen complexes significantly. However, the molecular machinery of the promoted effects is missing. Herein, a comprehensive investigation of styrene oxidation by a cobalt(III)-iodosylbenzene complex, [(TQA)CoIII(OIPh)(OH)]2+ (1, TQA = tris(2-quinolylmethyl)amine), in the presence and absence of triflic acid (HOTf) was performed using density functional theory calculations. Results revealed for the first time that there is a low-barrier hydrogen bond (LBHB) between HOTf and the hydroxyl ligand of 1, which forms two valence-resonance structures [(TQA)CoIII(OIPh)(HO--HOTf)]2+ (1LBHB) and [(TQA)CoIII(OIPh)(H2O-OTf-)]2+ (1′LBHB). Due to the oxo-wall, these complexes (1LBHB and 1′LBHB) cannot convert to high-valent cobalt-oxyl species. Instead, styrene oxidation by these oxidants (1LBHB and 1′LBHB) shows novel spin-state selectivity, i.e., on the ground closed-shell singlet state, styrene is oxidized to an epoxide, whereas on the excited triplet and quintet states, an aldehyde product, phenylacetaldehyde, is formed. The preferred pathway is styrene oxidation by 1′LBHB, which is initiated by a rate-limiting bond-formation-coupled electron transfer process with an energy barrier of 12.2 kcal mol-1. The nascent PhIO-styrene-radical-cation intermediate undergoes an intramolecular rearrangement to produce an aldehyde. The halogen bond between the OH-/H2O ligand and the iodine of PhIO modulates the activity of the cobalt-iodosylarene complexes 1LBHB and 1′LBHB. These new mechanistic findings enrich our knowledge of nonheme chemistry and hypervalent iodine chemistry and will play a positive role in the rational design of new catalysts.
AB - Introduction of Brønsted acids into biomimetic nonheme reactions promotes the oxidative ability of metal-oxygen complexes significantly. However, the molecular machinery of the promoted effects is missing. Herein, a comprehensive investigation of styrene oxidation by a cobalt(III)-iodosylbenzene complex, [(TQA)CoIII(OIPh)(OH)]2+ (1, TQA = tris(2-quinolylmethyl)amine), in the presence and absence of triflic acid (HOTf) was performed using density functional theory calculations. Results revealed for the first time that there is a low-barrier hydrogen bond (LBHB) between HOTf and the hydroxyl ligand of 1, which forms two valence-resonance structures [(TQA)CoIII(OIPh)(HO--HOTf)]2+ (1LBHB) and [(TQA)CoIII(OIPh)(H2O-OTf-)]2+ (1′LBHB). Due to the oxo-wall, these complexes (1LBHB and 1′LBHB) cannot convert to high-valent cobalt-oxyl species. Instead, styrene oxidation by these oxidants (1LBHB and 1′LBHB) shows novel spin-state selectivity, i.e., on the ground closed-shell singlet state, styrene is oxidized to an epoxide, whereas on the excited triplet and quintet states, an aldehyde product, phenylacetaldehyde, is formed. The preferred pathway is styrene oxidation by 1′LBHB, which is initiated by a rate-limiting bond-formation-coupled electron transfer process with an energy barrier of 12.2 kcal mol-1. The nascent PhIO-styrene-radical-cation intermediate undergoes an intramolecular rearrangement to produce an aldehyde. The halogen bond between the OH-/H2O ligand and the iodine of PhIO modulates the activity of the cobalt-iodosylarene complexes 1LBHB and 1′LBHB. These new mechanistic findings enrich our knowledge of nonheme chemistry and hypervalent iodine chemistry and will play a positive role in the rational design of new catalysts.
UR - http://www.scopus.com/inward/record.url?scp=85149375170&partnerID=8YFLogxK
U2 - 10.1021/jacs.2c12307
DO - 10.1021/jacs.2c12307
M3 - Article
C2 - 36867878
AN - SCOPUS:85149375170
SN - 0002-7863
VL - 145
SP - 5739
EP - 5749
JO - Journal of the American Chemical Society
JF - Journal of the American Chemical Society
IS - 10
ER -